JPS5849607B2 - Cooling stave with non-fused double cooling pipes - Google Patents

Description

Detailed Description of the Invention The present invention relates to improving the structure of a cooling stave for a metallurgical furnace such as a blast furnace. The purpose is to provide a cooling stave that can be completely prevented from causing damage.

The walls of metallurgical furnaces such as blast furnaces were generally constructed of refractory bricks, and appropriate cooling boxes were installed at various places through the outer shell, but as blast furnaces have become larger in recent years, the heat capacity inside the furnace has increased. The number of blast furnaces has increased dramatically, and cooling using a cooling box is no longer sufficient, and recently, cooling staves have been adopted in most blast furnaces.

Needless to say, the characteristics required of this cooling stave are that it has high heat resistance and wear resistance, and that it must maintain the strength of the furnace wall over a long period of time. It also has the optimum conditions such as effective heat exchange on the surface, heat transfer efficiency between the cooling water pipe inside the stave and the stave base material, and prevention of propagation of cracks that occur in the stave base material to the cooling water pipe. The manufacturing process must also be simple.

Therefore, the cooling tape that has been proposed so far is
There are so-called non-fusion types with a single cooling pipe and non-fusion between the stave base material, those with double cooling pipes and non-fusion with the stave base material, and fusion types. However, the treatment for preventing fusion between the cooling pipe and the stave base material is often performed by providing a non-metallic layer on the surface of the cooling pipe and then casting it with the stave base material.

However, in the cooling staves that have been put into practical use and implemented in the past, the heat transfer efficiency between the cooling pipe and the stave base material is poor, resulting in melting and loss of the stave base material.
Due to cracks that occur in the stave base material that spread to the cooling pipes due to insufficient non-bonding treatment, it has been regrettable that the effectiveness of the cooling tape has not been fully utilized.

This invention provides a cooling stave that eliminates the various deficiencies of the conventional cooling stave described above, has high heat resistance and wear resistance, and is capable of maintaining the strength of the furnace wall over a long period of time. It is.

That is, in this invention, the C equivalent of the inner tube is 0.20 to 0.38,
A thickness of 0.08 to 0.2 mm is provided on the outside of a drawn double-walled steel pipe whose C equivalent is 0.15 to 0.25. This is a cooling stave equipped with a non-fused double cooling pipe made of a 25 mm alumina coating and then cast with spheroidal graphite cast iron.

Next, the reason for the above-mentioned precautions in the cooling stave of the present invention will be explained.

According to the classification of conventionally known cooling staves, the cooling tape of this invention falls into the double cooling tube type with no external fusion. One of the features is that different materials are selected for the inner and outer tubes to prevent material deterioration due to carburization.

That is, the inner tube contains 0.20 to 0,38 preferably 0.23 to 0 in terms of C equivalent.
．． 35 steel, and convert it into C equivalent for the outer tube? and 0.15 to 0.25 preferably << is 0.17 to 0.2
This method uses steel with a composition of 0.0 and is made into a double tube in order to increase the degree of adhesion between the inner and outer tubes, which is then drawn out by cold drawing or the like to form a double tube.

To explain this from another perspective, even if the inner tube is unable to cool, which is the original mission of the cooling stave, even if a crack occurs in the cast body, which is the base material of the stave, the outer tube may have cracks or other cracks due to the ripple effect. Even if damage occurs, the tensile strength must be 40 kg/mm” or more so that the work can be carried out without any problems.On the other hand, the outer tube must have a tensile strength of 40 kg/mm” or more to ensure workability such as cold drawing when making a double tube. In addition, in the event that there is a missing or thin part of the Aluna coating (although such a thing almost never occurs), even if carburization occurs from the cast body of the stave base material at that location. It is necessary to use a soft material with low carbon so as not to cause any problems.

For this reason, the C equivalent in the steel composition of the inner and outer tubes was limited as described above.

The chemical and mechanical properties of an example of a preferred steel for the inner and outer tubes of this invention are shown in Table 1 below.

The reason why the C equivalent of the outer tube is limited to the above range is that the alumina coating formed on the outside by a thermal spraying method has a thickness of O. This is to deal with the possibility of carburization caused by making the thickness OS ~ 0.25 mm. If a C equivalent exceeding the above range is used, embrittlement may occur due to carburization, so it is not preferable. This is because a material having a C equivalent of less than 10% has a disadvantage of being too weak in strength.

In addition, the C equivalent of the inner tube was limited to the above range because although the inner tube is physically crimped to the outer tube, their metallographic structure is completely different. If a crack occurs in the outer tube, the non-fused layer will provide temporary crack prevention, and even if this non-fused layer does not prevent the crack from propagating and the crack spreads to the outer tube, the inner This is because the pipe needs to be strong enough to stop it.

The C equivalent of the steel for the inner and outer tubes is limited not only in consideration of carburization prevention and strength as described above, but also in terms of workability such as drawing processing for forming double tubes, and is a combination of strengths that will not cause unreasonable problems. Needless to say.

Another feature of the present invention is that the thickness of the alumina coating, which is the non-fusion layer formed on the outside of the double cooling tube, is limited to an optimum range.

As already mentioned in the explanation of the prior art at the beginning, it is well known that surface treatments such as clay, alumina, zirconia, or other materials are applied to the outside of the cooling metal tube to form a non-bonding layer.
In addition to the selection of the steel material of the drawn double cooling pipe in this invention as described above, the material and thickness of the coating forming the non-fusion layer are extremely important.

Therefore, in this invention, alumina spraying is used as a coating to form a non-bonding layer, and the thickness is set to 0.08 to Q. 25mm
The range of

This alumina thermal spraying was adopted because the thickness of the coating layer can be made thinner and its heat transfer efficiency is superior to other materials. This is because the stave base material is not replaced, which may lead to melting and damage to the stave base material.Also, if the OD is less than 8, the heat transfer efficiency is good, but there is a risk of carburization of the outer tube, and the outer tube becomes brittle. This is because it may ultimately have an adverse effect on the inner tube.

FIG. 1 is a graph showing the relationship between the thickness of the alumina spray coating and the heat transfer coefficient between the cooling pipe and the casting of the stave base material.

As is clear from this figure, the thickness of the alumina coating is inversely proportional to the heat transfer coefficient between the cooling pipe and the casting, and it changes rapidly between 0.1 and 0.2 degrees of coating thickness. From this point of view, the necessity of limiting the thickness of the alumina coating in this invention can be understood.

The chemical composition and mechanical properties of an example of the spheroidal graphite cast iron used for casting as the stave base material in this invention are shown in Table 2 below.

Next, the chemical properties and mechanical properties of preferred embodiments of the dual cooling tube of the Q invention are shown in Table 3 below.

? The inner and outer tubes described above are cold drawn to form a double tube, the degree of adhesion between the inner and outer tubes is increased, and an alumina coating with a thickness of 0.14 mm is provided on the outside of this double cooling tube by alumina spraying, and then the above spheroidal graphite is applied. A cooling stave of a normal shape was manufactured by casting with cast iron.The casting temperature in this case was set in the range of 1245±15°C, taking into consideration the thinness of the alumina coating as described above.

If the casting temperature is lower than this, the gap between the pipe and the casting will become wider and the heat transfer efficiency will decrease; if the temperature is higher, on the other hand, the alumina coating will melt and a fused state will easily occur between the pipe and the casting. There is a risk of carburization.

In addition, when making a double pipe, the heat transfer coefficient when the inner pipe is made of black bark material and the double pipe is made by cold drawing and then cast is as follows:
2 0 0 0 Kcal/rr? hr ℃,
When the inner tube is made of pickled material and made into a double tube by cold drafting and cast, the heat transfer coefficient is 5000Kcal/h.
r'C, and of course the inner tube should be made of pickled material.

Photo 1 is a microscope (X 1
0 0 ), and Photo 2 is a similar photo when the thickness of the alumina coating was set to 0.14 mrn.

Photo 3 shows the steel structure of the cross section at the center of the wall thickness of the outer tube when the thickness of the Aluna coating is 0.05 mm.
), and Photo 4 shows the thickness of the above alumina coating being 0.
．． This is a similar photograph taken when 14mrn was used.

It will be understood that carburization occurs in the case of the alumina coating of 0.05 mm in Photo 1, but there is no carburization in the case of this invention with the alumina coating of 0.14 mm in Photo 2.

The cooling stave equipped with non-fused double cooling pipes of the present invention configured as described above can approximate the flow of heat near the cooling pipes as heat transfer in a one-dimensional cylinder, and the heat transfer rate of the cooling pipes can be reduced. By setting a predetermined value according to conditions, pipe diameter, etc.
This can be achieved without compromising cooling capacity.

Therefore, a cooling stave with sufficient cooling capacity is provided, and even if a crack occurs in the cooling stave body due to thermal shock or other reasons, the non-fusion layer prevents the crack from propagating to the pipe. Furthermore, in the unlikely event that the unfused layer is defective and there is a fused spot between the stave base material casting and the outer tube, and a crack propagates from there to the outer tube, the inner and outer tubes will remain unfused. Therefore, the crack will not propagate to the inner pipe.

In addition, this naturally provides double safety against leakage of cooling water, and the cooling stave ensures heat transfer resistance between the casting of the main body of the staple, the cooling pipe, and the cooling water, thereby extending the life of the furnace body. This has the effect of prolonging the time.

Incidentally, even after three years of operation, the blast furnace equipped with the cooling stave according to the above-mentioned embodiment of the present invention has not encountered any problems, and has greatly contributed to the stable operation of the blast furnace.

In addition, the cooling stave of this invention is not only used in blast furnaces.
Needless to say, it can be applied to other furnace equipment as a cooling plate with cooling pipes cast into it.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the heat transfer coefficient between the cooling pipe and the casting and the thickness of the alumina coating. Figure 2 is a micrograph showing the steel structure of the cross section of the outer surface of the outer tube when the thickness of the alumina coating is 0.05 mm, and Figure 3 is a photomicrograph showing the steel structure of the outer tube when the thickness of the alumina coating is 0.14 mvt. FIG. 4 is a microphotograph showing the steel structure in the cross section of the outer surface of the tube, and FIG. The figure is a micrograph showing the steel structure at the center of the wall thickness of the outer tube when the thickness of the alumina coating is 0.14 mm.

Claims (1)

[Claims] 1. An alumina coating with a thickness of 0.08 to 0.25 mm is provided on the outside of a drawn double-walled steel pipe in which the inner tube has a C equivalent of 0.20 to 0.38 and the outer tube has a C equivalent of 0.15 to 0.25. Next, a cooling staff with non-fused double cooling pipes made of spheroidal graphite cast iron.